Potting treatment and the like by e.g. an epoxy resin or a silicone resin have been widely employed for the purpose of insulation, moisture-proofing, water-proofing, or vibration-proofing for electronic components. Further, along with e.g. downsizing, increase in density and increase in power of electronic components in recent years, as a potting material therefor, e.g. an epoxy resin and a silicone resin into which an inorganic filler having thermal conductivity such as silica or alumina is incorporated for the purpose of releasing heat generated from the electronic components, have been used. Further, for semiconductor packages also, a means for heat dissipation has been employed by bonding heat spreaders or heatsinks for the purpose of protecting e.g. IC chips from heat generation. Similarly, along with downsizing and increase in density of electronic components, bonding by an adhesive, not by screws, has been carried out, and as the adhesive, e.g. an epoxy resin and a silicone resin having thermal conductivity have been used.
An epoxy resin into which an inorganic filler is incorporated has excellent heat insulation properties and water resistance, but its cured product has a very high modulas, whereby a stress is likely to be applied to e.g. components by e.g. heat shock, which may cause cracks or separation. Further, in the case of a two part epoxy resin, there is a risk of insufficient curing if the blend ratio of the curing agent is mistaken. On the other hand, in the case of a one part epoxy resin, a heating apparatus is required in many cases and the curing time tends to be long, such being disadvantageous in view of further labor saving and energy saving and shortening of operation time.
Further, a silicone resin has been known as a RTV (room temperature vulcanizable) rubber, and its cured product has low hardness and is excellent in low temperature resistance and heat resistance. However, a silicone resin has such drawbacks that a low molecular siloxane contained as an impurity may cause continuity failure or abrasion of electric contacts, and is expensive also.
On the other hand, heretofore, an acrylic resin has been widely used in the field of molding materials, coatings and adhesives by virtue of having good durability and being environmentally friendly. Such an acrylic resin may be obtained in such a manner that an organic peroxide as a polymerization initiator is added to an acrylic monomer or oligomer, and radicals are generated by thermolysis of the organic peroxide to polymerize the acrylic monomer or oligomer.
An acrylic resin is characterized in that it is generally less extendable and its cured product is hard. Further, if an inorganic filler is incorporated, it will have a high modulas in the same manner as an epoxy resin and be poor in heat cycle resistance. However, in recent years, by e.g. use of an acrylic monomer to impart flexibility, an acrylic resin being flexible and having a low modulas equal to a silicone resin has been developed.
However, even with respect to such an acrylic resin having flexibility imparted, if an inorganic filler to impart thermal conductivity is incorporated in a large amount, the viscosity tends to increase, and when an electronic component is sealed or bonded, workability tends to be poor and it cannot sufficiently infiltrate into the component, or the sealed or bonded resin itself may contain bubbles, and no sufficient heat dissipation properties can be secured (Patent Documents 1 and 2).
Patent Document 1: JP-B-54-28178
Patent Document 2: JP-A-2002-308919